Mineralogy - Petrology
Department of Mineralogy and Petrography
Innrain 52f
6020 Innsbruck
In the Mineralogy - Petrology department, we use chemical microanalysis methods to study natural and synthetic materials with regard to their main and trace elements (in cooperation with international research partners also with regard to their isotopic composition). The data obtained can provide direct information about the origin of the material (provenance analysis) or be used to calculate distribution coefficients, which in turn can be used as geological thermometers or barometers or for modelling geological cycles.
The natural materials come from almost every conceivable environment, from alpine rocks and river sediments to volcanic material from deep within the Earth and cosmic material such as meteorites. High-pressure and high-temperature experiments facilitate conclusions about the formation conditions and answering the question which conditions prevailed in order to obtain the phases and their element distribution observed in nature. Knowledge of the formation conditions enables the targeted synthesis of material.
The range of methods includes electron beam microprobe, Raman spectroscopy, FTIR spectroscopy, and high-pressure equipment.
Quartz is the second most common mineral in Earth's crust and an important component of many types of rock. Quartz crystallises mainly in water-bearing granite systems, where the nominally anhydrous quartz incorporates water into the crystal lattice as defects through coupled exchange reactions. Defect-water contents in Variscan granites (0.3 billion years) are an order of magnitude higher than in Proterozoic granites (0.9-1.8 billion years) from Scandinavia. The water content is reflected in recent sediments and post-Variscan sedimentary rocks and shows a SW-NE gradation. Higher OH contents are preserved in the 1.4 billion year old sandstone from Dalarna/Sweden (Stalder 2021).
Mineral reaction fringes contain a wealth of information that can be used to decipher the conditions during transformation. One of the most important parameters for the development of fringe microstructures is the presence of water. Reaction fringes have the potential to ‘notice’ variations in the amount of water at grain boundaries, allowing them to be used as sensitive ‘geohygrometers’. Furthermore, the effect of water on the relative layer thicknesses may allow to distinguish between water-unsaturated and water-saturated conditions during transformation (Franke et al. 2023).
Calcium phosphates are important carriers of phosphorus, halogens and incompatible trace elements in Earth's crust and mantle. The high-pressure phase Tuite is stable up to at least 25 GPa (and thus up to a depth of at least 700 km) and 1700 °C. Beyond the stability limit of majorite garnet, Tuite is therefore the most important crystalline phosphorus carrier in the upper part of the lower Earth's mantle (Pausch et al. 2024).
